Dale and Marigold are hardly strangers at this point though. Dale's been over for anime night, they've done some pretty intense spit-swapping at the Coffee of Doom, and both have finally admitted their attraction for each other (in the most awkward way, likely). It's still just a little bit creepy, but it's not like this date is the first time they were going to be spending together. Then sticking around would have been massively creepy. And of course, Dale's first reaction was in fact to leave and let Marigold sleep it off, but she quite strongly insisted...
I'm really not seeing that Mari was creeped out by this... She was just hyper anxious that she ruined another night/chance with Dale. But he did a stand up thing. Made sure she was okay, and spent the night hanging out with Momo.